The reaction of particulate solids with gases and/or vapors at elevated pressures are of increasing importance in recent years and such processes as gasification, hydrogasification an hydrocarbonization of coal have taken on greater significance due to the worldwide petroleum shortage. In many of these reactions, the solids must be brought into a pressurized reaction zone.
At present, two solids feeding systems are conventionally used for feeding particulate materials such as coal into reaction zones, viz., (1) pressurized lock hoppers and (2) systems wherein a slurry of the particulate material is made using a liquid such as water or low boiling hydrocarbons. The principal drawbacks of the first system are the intermittent batchwise operation employed and the high power requirements for the compression of the gas needed to pressurize the lock hopper and displace the solids. The disadvantage of the second system is the high requirement of heat for the evaporation of the slurrying liquid and the usual need for the separation of the vapor from the solids. The temperature required for the evaporation of the slurrying liquid may have a deleterious influence on the properties of the solids and the decomposition products may contaminate the separate vapor of the slurrying liquid.
Methods for feeding solids to a reaction zone have also been proposed wherein a compact column is used (see, e.g., U.S. Pat. Nos. 2,726,137; 2,761,575; 2,837,467; 2,713,949; and 2,854,157). In general, this approach suffers from high operating costs and power requirements. In addition, the use of fluidized columns in feeding solids into a reaction zone has also been proposed. This approach provides for maintaining the fine solids in a stationary position or requires the withdrawal of fluidizing gas from the column (see, U.S. Pat. Nos. 2,925,928 and 2,753,061). Again, such approaches suffer disadvantages relating to high energy requirements, similarly to the methods discussed above.
It will be appreciated that while the systems discussed above are the systems conventionally used in feeding coal for the purposes outlined, other feeding techniques for other more general purposes are, of course, widely known and used. Insofar as these techniques bear on the present invention, it is noted that the broad concept of utilizing column pressure in the feeding of materials in general is not novel and reference is made to U.S. Pat. Nos. 2,723,883; 2,770,503; 2,919,159; 2,922,611; and 3,062,589 for examples of systems using this general technique.